Idiopathic dilated cardiomyopathy, formerly called congestive cardiomyopathy, is a syndrome characterized by cardiac enlargement and congestive heart failure. Although no etiology is definable in most cases, the congestive cardiomyopathy is believed to represent the result of myocardial damage caused by toxic, metabolic or infectious agents. Diagnosis of this disease depends solely on the exclusion of other possible causes at a late stage of the disorder. Nearly 40% of the patients receiving heart transplants suffer from idiopathic dilated cardiomyopathy.
Abnormal modulation of intracellular calcium has been proposed as the key mechanism underlying the systolic and diastolic dysfunctions that accompany heart failure associated with cardiomyopathy. Recently, several studies have documented the pathogenetic role of abnormal sarcoplasmic reticulum (SR) function in various cardiomyopathies. For example, Ca.sup.++ -ATPase expression is decreased in patients having end-stage heart failure caused by the various cardiomyopathies.
The relationship between systolic function and intracellular calcium is not consistent among the different animal models that have been used to study cardiomyopathies. However, an excellent correlation has been demonstrated between systolic dysfunction and decreased availability of activation calcium in Syrian hamsters having end-stage dilated cardiomyopathy. The mechanism underlying abnormal intracellular calcium regulation in cardiomyopathies has not been explained previously.